The present invention relates to apparatus and methods for analysing surfaces. In particular, the present invention relates to apparatus and methods for analysing surfaces which, in use, are subject to drag. The present invention also relates to methods for determining surface-related drag of surfaces.
Surfaces that are subject to aerodynamic or hydrodynamic drag are often contaminated by dirt, dust, ice, particulates or other matter present in the environment. The surface may, additionally or alternatively, have intrinsic roughness either because a structure and/or coating with such roughness has been applied (e.g. shark skin-type structures) or because of weathering or abrasion/ablation in the environment (e.g. from particulate impact). Polish may have been applied to modify and smooth surfaces which have developed undesirable roughness. Roughness of the surface or removal of polish by weathering etc. may reveal undesirable surface structure which can lead to increased drag.
Contamination or roughness can adversely affect the performance of surfaces subject to drag. In the case of high speed vehicles such as high speed trains and aircraft, contaminated and/or rough surfaces can increase drag, resulting in higher fuel consumption and can sometimes affect aerodynamics and flight performance. These problems may be particularly troublesome on aircraft surfaces and also wind turbine blades.
Washing of the surfaces to remove contamination, polishing surfaces or otherwise maintaining the surface can be difficult and expensive with large vehicles such as aircraft or difficult to access surfaces such as in wind turbines having to be temporarily taken out of service. Thus maintenance should only be undertaken when necessary. It would therefore be advantageous to determine the extent and effect of the surface structure, for example roughness, polish or contamination, and in particular the effect of the surface structure on drag.
There have been attempts to determine surface conditions, including the extent of the contamination, of surfaces in aircraft and on other aerodynamic surfaces.
EP-A-2 492 195 discloses a technique of ensuring hygienic conditions in interior spaces on board e.g. aircraft.
US-A-2012/085868 discloses an aircraft icing detector using laser probes to determine the surface contour of the depth of airfoil icing in the measurement area.
WO-A-2004/061438 (Boeing) discloses measuring amounts of contaminants on a surface with IR spectroscopy using two or more wavelengths.
EP-A-1 466 827 discloses a fibre optic technique for detecting ice on e.g. a wing or other surface using infrared in the water absorption bands.
There have been other solutions proposed including by treating the aerodynamic surfaces with coatings to change their surface properties.
WO-A-2009/085418 (General Electric) discloses self-cleaning aerodynamic surfaces and the use of coatings to provide such surfaces.
There is, nevertheless, a need to provide apparatus and methods to address these problems.